Protein trafficking is an active process in which proteins are re-located from one region of a cell to another. Membranes and their protein components are constantly being turned over through a mechanism that has multiple components and pathways. One of the mechanisms of modulating the activity of cell surface receptors, such as G protein-coupled receptors (GPCRs) and the Epidermal Growth Factor receptor (EGFR), is through receptor endocytosis. For GPCRs, ligand-induced receptor endocytosis can drive receptors removal from the PM through specialized compartments like clathrin-coated vesicles, which involve the recruitment of the endocytic adaptor β-arrestin to liganted receptors (Claing, Laporte et al. 2002). Internalizing receptors can be directed into divergent lysosomal and recycling pathways, producing essentially opposite effects on the strength and duration of cellular signaling via heterotrimeric G proteins, and can also promote distinct signalling events from intracellular membranes through the signalling scaffolding of β-arrestins (Hanyaloglu and von Zastrow 2008; Posner and Laporte 2010). Therapeutic advantages have been proposed for drugs promoting the intracellular targeting of GPCR/β-arrestin complexes, while for some receptors their recycling to the PM is also essential for adequate maintenance of physiological responses.
Thus, simple and reliable systems for monitoring receptor trafficking are key to study the mechanism of receptor endocytosis and to develop efficient therapeutics acting on cell surface receptors such as GPCRs. For instance the Angiotensin II type 1 receptor (AT1R) has attracted significant attention for drug development, because of its involvement in the development of cardiovascular diseases, including hypertension, hypertrophy, fibrosis and atherosclerosis (Hunyady and Catt 2006), and because ligands, which have cardioprotective function can also promote internalization of receptors and intracellular AT1R/β-arrestin signalling complexes. Great advantages can thus arise from developing assays efficiently assessing in a quantitative and high efficiency manner drugs' propensity to induce the internalization of receptors such as GPCRs.
The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety.